23 Setting up Communication between Wireless Networks
In case an infrastructure wireless network design is being used for setting up communication between two networks, the two key parts of the network are:
- The wireless client (known as the station or STA in short)
- The Access Point (AP in short) which acts as the bridge between the STA and the network.
The step that precedes transmission is communication between the wireless AP and the client. This initial step consists of
- Association: The moment a wireless adapter is turned on, the client adapter starts to scan for wireless AP's or other wireless devices (in an ad hoc mode). In the infrastructure mode the wireless AP can be chosen by the user. This exercise of choice can also be automated depending on the SSID, strength of the signal and error rate. Then the wireless adapter switches to the assigned channel of the wireless AP that has been selected. The AP negotiates the use of the port.
Every time the signal is dropped at a level below acceptability the adapter starts to scan for another AP with a stronger signal. The process is repeated with the new AP and is termed as re-association.
- Authentication: Once the association process gets over starts the process of authentication. The first step in authentication is application of keyed security measures. AP's can be set for two kinds of authentication:
- Shared key authentication: In this the client has to deliver up to the security requirements before communication with AP can start. o Open authentication: This is the default key setting and in this authentication enables access only with the SSID or /and with the WEP key. The shortcoming of this method is in case, the other protection or mechanism is not in place the system become vulnerable to intruders.
Once security requirements are complied with, IP level communication is established and Ethernet networking starts.
Many components are combined for setting up effective wireless communication between two devices. These components are required to be configured on both the client and the AP. These devices are:
- SSID/ESSID: These are required in both the cases - ad hoc as well as infrastructure. It is a client identification and essential while communicating with a particular base station.
- Wireless Channel (RF): It is also an important part of wireless communication. It refers to the band of frequency that is used while establishing wireless communication.
Security Features: Under the umbrella of 802.11 standards, security is provided fro by using two methods: